Various vehicle systems may require an antenna for mobile phones, satellite radio, terrestrial radio, and/or global positioning systems. Providing several antennas on a vehicle is costly and aesthetically displeasing. The antennas are preferably low profile and small in size.
Terrestrial communications systems require the transmission and/or reception of vertical polarized signals. Terrestrial communications systems may require reception and transmission of radio frequency (RF) signals in multiple bands. For example, vehicle systems such as mobile phones and remote assistance services transmit and/or receive vertical polarized signals in multiple bands.
Mobile phone and remote assistance services typically require communication in both the Advanced Mobile Phone System (AMPS) and the Personal Communications Services (PCS) bands. A dual band antenna that communicates in both the AMPS (824 to 894 MHz) and PCS (1.85 to 1.99 GHz) bands requires a large frequency separation. In one method, a patch antenna is used for dual band communications. However, a patch antenna transmits/receives most of its energy perpendicular to the plane of the patch antenna, which is not suitable for terrestrial communications.
In another method, a planar monopole antenna provides dual-band terrestrial communications. Monopole antennas operate due to multiple reflections between the ends of the antenna and a feed point, which creates a resonance. However, higher-order resonant frequencies of monopole antennas are typically fixed relative to the fundamental resonance. Therefore, planar monopole antennas cannot typically operate in both the AMPS and PCS bands.